All things aside, how big could a black hole actually get?

Nabeshin

I do not understand this logic at all. If some quantum gravitational correction produces some bounce near the singularity of a big crunch, the mechanism should work equally well for any mass. That is, it would resolve the singularity of any size black hole into a non-singular object. Even so, it seems very difficult to escape that there still must exist an event horizon, and there is no reason to suppose that this disappears at any particular size.

Radrook

Please show me where I said that the event horizon disappears.

Nabeshin

Well you did not, you said that there would be a 'big bang'. I simply assumed this meant the structure of the hole, i.e. the horizon, would be eliminated by this. What did you mean, then?

Radrook

As you already know, the Big Crunch theory postulated that universal expansion following the BB halts, matter reverses direction, collapses into a singularity and another Big Band occurs ad infinitum The mechanism behind this they did not know but simply tossed the idea around as feasible.

As the black hole caused by the crunch grew its event horizon would expand to gargantuan dimensions thus accelerating the influx of material. Eventually all matter would be inexorably drawn in regardless of where that matter is located. Ultimately the whole infernal thing would collapse back into the infinitely small primordial cosmic egg that it had been and somehow Big Bang all over again.

But since infinitely dense and infinitely-small singularities are described as retaining and event horizons, then the question is, now that YOU mention it, whether this one would also.

Please note that this singularity involves not only the collapse of matter but of space time itself leaving nowhere to extend an event horizon into. If indeed we imagine that an event horizon remains, then we would be forced to explain just where such a horizon would be extending into since space has disappeared into the singularity. This is totally unlike the regular singularities where the surrounding universe remains intact leaving a place where an event horizon can indeed manifest itself.

So since the question is whether a fed black hole can ever reach a point where it rebounds or regurgitates, and a black hole harbors a singularity, then this Big Crunch or Oscillating universe theory seems to indicate that it might. That is unless the qualitative difference between it and a regular infinitely small singularity makes the conclusion untenable which very well might be the case.

Chronos

When you attempt to apply the laws of thermodynamics to a cyclical universe model, you are immediately confronted with serious issues.

Radrook

I am not personally attempting nor proposing anything. In any case, can you please be more specific.

Chronos

When you propose a cyclical universe, you inherit the burden of explaining how it conforms to the laws of thermodynamics.

Radrook

In other words, you see burdensome thermodynamics problems inherent in the once-proposed cyclical-universe idea.

Radrook

Here a couple of videos relevant to the thread.

Journey Into a Black Hole
http://www.youtube.com/watch?v=eI9Cv...feature=fvwrel

Black Holes and Galaxies
http://www.youtube.com/watch?v=gib2i...feature=relmfu

Antiphon

You don't need to have a big crunch in principle do you?

If all the matter (dark and light) and energy (dark and light) in the universe (best guess of course as to the quantity) were dropped into one black hole, what would be the radius of the event horizon?

I estimate (without having done the math) about 1 galactic radius.

Radrook

Cyclic models such as the Big Crunch demand that the cycles be infinite. But that in turn requires that we deal with the problem of heat death caused by entropy. In fact, that original cyclic model was discarded exactly because of it since heat death would bring the oscillations to a halt. But other cyclic models such as the Steinhardt–Turok model and The Baum–Frampton model are considered more feasible by some because they evade the heat death scenario in various ways. However, they too create problems that elude a theoretical solution. In any case, at present evidence indicates that expansion is accelerating while deceleration and reversal have no such observational support.







Cyclic Models
http://en.wikipedia.org/wiki/Cyclic_model



Interesting estimate. Did you include the undetectable part of the universe? By undetectable I mean the part that is beyond detection due to the universal expansion.